ISOLATES

From Big Medical Encyclopedia

ISOLATES — rather small populations of people (100 — 1000 people) with the insignificant level of marriage immigration. In order that population could be classified as well as., conditions of marriage isolation shall exist throughout several (not less than 5 — 10) generations. The term «isolate» has relative character; absolute And., apparently, never meet, and apply it to the populations which were more closed than usual.

Both physiographic, and social and religious factors, traditions and so forth can act as the reasons of marriage isolation at the person. However it is undoubted that in creation and maintenance And. throughout all history of mankind and in their disintegration socio-economic factors, features of economic way, a social order, religious and national traditions are primary.

Infinitely big populations in which the parent gametes creating zygotes of the next generation happen statistically are called panmiksny; respectively accidental crossing carries the name of a panmixia. However infinitely big populations only mathematical abstraction therefore opposition of isolation and a panmixia is relative.

The main quantitative criterion for reference of population to category I. the coefficient is inbreeding (see), i.e. the size reflecting degree of likeness of the people making population (if he is great — 0,03 — 0,001), or to category of panmixias (if it is small — 0,0001 — 0,00001).

The coefficient of inbreeding of the nek-ry person defined from its family tree, and average coefficient of inbreeding of all members of population are used by most of researchers as a measure of an inbrednost of the person or population. However reliability of this assessment depends on completeness of collecting genealogical material (number of the captured generations).

By origin And. it is possible to divide into three groups conditionally: relic And., remained since the Neolithic when all mankind represented a number of the small isolated populations (system of isolates of Siberia, South America, Australia); And., arisen during the period from antiquity before the early Middle Ages — the populations formed in areas with small population density (the North of Scandinavia, the European North of RSFSR, mountain areas — Dagestan, Pamir, the mountains of Japan); so-called religious And. (hatterita and dunker in the USA, Samaritans of Israel, a habbanita of the Southern Arabia, Karaites of Lithuania). Part of these And. arose only 300 — 500 years ago, however strict distinctions between these three categories of the isolated populations cannot be carried out by an example to what rural exclusive isolates of India can be.

The main reason for attention of geneticists and physicians to studying of the isolated populations is course in them genetiko-automatic processes, i.e. drift of genes. Understand random change of the genetic constitution of population as drift of genes, to-rogo, e.g., small number of this population therefore drift of genes does not conduct to genotypic adaptation by Wednesday can be the cause. The size of population is less, the in it process of drift of genes proceeds more intensively. This process leads to decrease in frequency of occurrence or even to full loss of one of alleles of a nek-ry locus and increase in frequency of occurrence of other allele of the same locus. As a result of drift of genes everyone And. it is characterized by the gene frequencies, in some cases differing from next markedly And., related community of an origin. These differences can reach level international or interracial.

It is necessary to emphasize that drift of genes is accidental in relation to phenotypical effect of the «drifting» alleles. Therefore the frequency of harmful alleles can sometimes increase. It is especially characteristic of recessive alleles which show the phenotypical effect only in a homozygous state, and heterozygous carriers are not affected by them natural selection. The big frequency of kinship marriages characteristic for And., increases probability of a meeting of two such alleles in one zygote, otherwise, in And. frequency of emergence of hereditary diseases can be increased. Fixed interest of doctors and geneticists in the isolated populations is also explained by it.

And. represent ample opportunities for studying of phenotypical polymorphism of separate hereditary diseases (see) on extensive a wedge, material, and also for the analysis of genetic heterogeneity of externally uniform forms. Studying of a series I. allows to describe a wide range of hereditary diseases, to register considerable number earlier not known patol, genes since everyone And. possesses own nozol, a profile. It is possible to give long-term researches as an example V. Mack-Kyyuziky of group I. Amishes in the USA, in a cut it was succeeded to identify earlier not described recessive diseases, to obtain new data on multifactor diseases. The research of the isolated rural populations of Finland [H. R. Nevanlinna] allowed to find in some of them a large number of cases of the inborn nephrosis leading to death of children in the first weeks of life. Moreover, increase (as a result of drift of genes) even dominant diseases, a part from which (e.g., a generalized amyloidosis) out of the studied populations is not described, was found in these populations.

In the USSR research I. has long traditions. The attention of physicians geneticists is drawn by the isolated rural populations of the Central Russia, the Caucasus, Central Asia (V. V. Sakharov, N. P. Bochkov), relic isolates of Siberia and Altai (Yu. G. Rychkov).

That circumstance that along with is extremely important And., considerable the burdened hereditary diseases, with a large number of patients, meet also such in which the medicogenetic situation is rather favorable. Comparison among themselves And., similar or differing by origin, degrees of isolation, to terms of existence, influence of environmental factors, genetic burdeness, the role of these factors in formation of a gene pool of populations allows to estimate, and the received conclusions can have considerable predictive value. Therefore studying And. is one of essential problems of medical genetics.

As a rule, is exposed to a medicogenetic research not individual And., but group of the populations connected by a community of an origin. First of all before the researcher there is a problem of assessment of the size of each single population from group related and exchanging migrants, i.e. determination of the effective size of population. The effective size of population can be considered approximately equal its 1/3 qualification sizes. For the analysis of mutual isolation of the studied populations data on distribution feno-and genotypic frequencies of mendeliruyushchy markers (a blood group, serumal and erythrocyte enzymes etc.), data of ethnographic studying (surnames, patrimonial accessory), demographic data (duration of digenesis, the size of a family, migration), at last, history and ecology of the considered populations are used.

The medicogenetic research individual I. Genetiku-vrachu is of special interest reasonablly to receive the material characterizing full families. It is necessary for implementation of this requirement or a total medical research I., or, if he is too great, careful preliminary identification of all is hereditary the burdened families. Genealogical material should be collected it is total also on the most available number of generations. The qualified medicogenetic research cannot be executed without involvement of clinical physicians of various profile.

Assessment of a gene pool of mankind and its features in the isolated populations is necessary for advance planning of actions for health care since in And. concentration patol, genes takes place.

See also Genealogical method , Mendel laws , Inheritance , Population genetics .


Bibliography: Dubinin N. P. General genetics, M., 1976, bibliogr.; Makkyyusik V. A. Ancestral features of the person, the lane with English, M., 1976, bibliogr.; Rychkov Yu. G. System of ancient isolates of the person in Northern Asia in the light of problems of stability and evolution of populations, searches and decisions on the ways of population genetics, Vopr, antropol., century 44, page 3, M., 1973; Efroimson V. P. Introduction to medical genetics, M., 1968; G a v and 1 1 i-S f about of z and L. L. a. Bodme of W. F. The genetics of human populations of, San Francisco, 1971, bibliogr.

A. A. Revazov.

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